The present invention relates to a printer which is capable of performing a multi-color printing and a monochrome printing. The present invention also relate to a color image recording apparatus where image forming section are aligned in tandem and images of different colors are recorded in registration with one another on a print medium to form a color image.
Various documents are produced using computers, word processors, and other business machines and the documents are printed by printers connected thereto. Such printers include electrophotographic printer, thermal printer, wire-dot printer, and ink jet printer. These printers receive print data from their host apparatuses, and store the print data therein, reform the print data, and provide the reformed print data at predetermined timings to print engines. With color printers, the print data is edited according to color such as yellow, magenta, cyan, and black.
Color printers are often required to print documents whose print data is mostly characters in the form of a black-and-white image. Thus, many color image-recording apparatuses have a black-and-white printing function as well as a color printing function.
The aforementioned conventional art suffers from the following drawbacks.
Print data includes four items of data for four colors and the respective items of data are subjected to compression and expansion before being fed to print engines. For this purpose, color printers are capable of processing about four times as large an amount of data as monochrome printers.
Thus, when the conventional color printer prints black-and-white images, only a part of its high data-processing capability is used. This is not economical. One solution to increased printing speed in the monochrome printing may be to transferring the data at a speed four times as high as in the color printing. However, increasing data transfer speed by a factor of four needs a higher system clock frequency. Higher clock frequencies impose a noise problem.
A conventional color image recording apparatus has image forming sections for yellow, magenta, cyan, and black images. A print medium is fed one page at a time from a paper cassette. A carrier belt attracts the print medium with the aid of Coulomb force and transports the print medium from section to section. Each image forming section has a corresponding recording head with recording elements aligned in line in a traverse direction perpendicular to an advance direction in which the print medium is transported. As the print medium passes the image forming sections, the print heads record images of corresponding colors on the print medium on a line-by-line basis.
The image forming section for black image is usually located most downstream of the transport path of the print medium. In the monochrome printing, the print medium is transported through the yellow, magenta, cyan image forming sections to the black image forming section.
Accordingly, the print medium is transported in the monochrome printing at the same speed as in the color printing even though only the black image forming section operates to print images. This is inefficient.